This invention relates to an improved conductive coated transparent substrate as used in a touch screen, or a digitizer panel, or a substrate in an information display such as a liquid crystal display, a plasma display, a field emission display, an electroluminescent display, an electrochromic display, or a cathode ray tube display.
In the production of conductively coated transparent substrates for use in touch screens, digitizer panels or information displays such as those described above, it is desired that the screen, panel or display not only have a conductive coating providing electrical conductivity to allow activation of circuits, switches or other electrical devices controlled by the screen or panel, but also allow the maximum transmission of light so that the user of the screen, panel or display can easily read the information transmitted through the screen thereby allowing manual activation using the conductive coating layer. Typically, such screens, panels or displays make use of anti-reflective, thin film coatings or stacks to reduce or minimize glare while allowing optimal light transmission. However, the provision of a conductive coating layer on one side of a substrate including anti-reflective thin film stacks or coatings changes the optical characteristics of the coated substrate and can prevent maximized light transmission unless the anti-reflective thin films or stacks and conductive layer are properly designed, coordinated and prepared for one another.
In the past, anti-reflective, thin film coating stacks or multiple layers have been prepared either by vacuum deposition or wet deposition processes. Vacuum deposition is typically carried out through sputtering processes in which layers of thin films of materials such as metal oxides and metal halides are applied to a surface of a transparent glass or other substrate followed by a second, third, fourth or other layers which together minimize or eliminate glare due to interference. However, in order to prepare one side of such a substrate for receipt of a conductive coating layer, it is necessary that vacuum sputtering deposition of the layers on either side of such a transparent substrate be prepared differently causing greater manufacturing time and expense.
Alternately, thin film coatings making up anti-reflective stacks or multilayers can be applied by wet deposition processes including dip coating in which the substrate is dipped in a container of liquid solution while held in a position perpendicular to the solution surface. When cured such as by firing, such process results in substantially identical coatings of the same solution on either side of the substrate. Although angle dipping or dipping of a substrate in a solution when held at an angle to the solution surface is known [such as is described in xe2x80x9cInvestigations on the Angle-Dependent Dip Coating Technique (ADDC) for the Production of Optical Filtersxe2x80x9d, N.J. Arfaten et al., Journal of Sol-Gel Science and Technology 8, 1099-1104 (1997) (copyright) Kluwer Academic Publishers], such angle dipping has heretofore not been used to prepare an improved conductive coated transparent substrate as in the present invention.
Accordingly, it was desired to provide a more efficient, less expensive, reduced glare, conductive coated panel having optimal light transmission, as well as a method for applying anti-reflective thin films or stacks to a transparent substrate using wet deposition processes such as dip coating while allowing preparation of the layers differently on each side of the substrate so that one or both sides are prepared for receipt of an electrically conductive coating to provide optimal light transmission characteristics through the coated substrate for use in touch screens, digitizer panels, information displays and the like.
This present invention contemplates use of angle dipping to establish one or more layers such as a multilayer stack of the same material type of thin films on the two opposite (first and second) surfaces of a substrate, and with the film thickness of an individual thin film on the second surface being different (such as for example, thicker) than its corresponding thin film (of the same material composition) on the first surface. The angle of dipping of the substrate when establishing the various layers of the multilayer stack on the respective surfaces is adjusted so that, when an additional outermost transparent conductor layer (or any other additional layer or layers) is disposed on, for example, the outermost layer of the multilayer stack having the thinner individual layer thicknesses (compared to those on the opposing surface), visible light transmission through the coated panel is increased compared to the light transmission through that substrate coated only with the electrically conductive, transparent conductor layer.
In one aspect, the invention is a reduced glare, conductive coated panel comprising a transparent substrate having a first surface and a second surface, a first, multilayer, anti-glare, interference stack disposed on the first surface of the substrate, the first stack comprising a plurality of transparent, thin film layers, and a second multilayer, anti-glare, interference stack disposed on the second surface of the substrate, the second stack also comprising a plurality of transparent, thin film layers. The first of the layers in the first stack is positioned on the first surface and corresponds to the first of the layers in the second stack which is positioned on the second surface. The second of the layers in the first stack is positioned on the first layer and corresponds to the second of the layers in the second stack which is positioned on the first layer of the second stack. At least one of the layers of the first stack has a thickness greater than the thickness of the corresponding layer of the second stack on the second surface. Also included is a transparent conductive coating on at least one of the thin film layer of the first stack which is spaced farthest away from the first surface and the thin film layer of the second stack which is spaced farthest away from the second surface. Visible light transmission through the coated panel is increased as compared to the substrate coated only with the transparent conductive coating.
In preferred aspects of the invention, the transparent substrate may be glass or plastic, and the transparent conductive coating is applied to the second stack which has the thinner individual layers. Alternately, the transparent conductive coating may be applied to the first stack having the thicker individual layers. As yet another option, an electrically conductive coating may be applied to each of the first and second thin film stacks such that an electrically conductive coating is on each side of the coated substrate. Should the substrate have only a single, anti-glare, interference thin film on each of the opposite substrate sides, an electrically conductive coating may be applied over the single thin film layer on one or both of the opposite sides.
Additionally, each of the first and second thin film stacks may include a third transparent thin film layer positioned, respectively, on the second layer of each stack. Each of the layers of the first and second stacks has a refractive index with the refractive index of the second layer of each of the first and second stacks preferably being greater than the reflective index of the other layers in the respective first and second stacks. Further, the refractive index of the third layer of each of the first and second stacks is preferably less than the refractive index of the other layers in those stacks.
In other aspects, the material composition of the corresponding layers in each of the first and second stacks or on opposite sides of the substrate may be the same. For example, the first layers in each of the first and second stacks maybe formed from a combination of silicon dioxide and titanium dioxide with each of the first layers having a refractive index at the sodium D line in the range of from about 1.5 to about 2.0. In addition, the second layers of each stack may be formed from titanium dioxide and have a refractive index at the sodium D line of at least about 2.0. Additionally, the third layers of each of the first and second stacks may be formed from silicon dioxide and have a refractive index at the sodium D line of less than about 1.5.
In yet another aspect, where each of the layers of the first and second stacks has a refractive index, the refractive index of the second layer of each of these first and second stacks is greater than the refractive index of the other layers in the respective stacks.
In yet another aspect, the invention is a method for making a reduced glare, conductive coated panel comprising providing a transparent substrate having a first surface and a second surface, and forming a first transparent thin film layer on the first surface and a first transparent thin film layer on the second surface by dipping the substrate in a liquid solution of a precursor of a material for the first transparent thin film layers while maintaining the substrate at an angle to the vertical whereby the first layer on the first surface has a thickness greater than the thickness of the first layer on the second surface, and applying a layer of transparent electrically conductive coating over at least one of the first layer on the first surface and the first layer on the second surface.
In preferred aspects of the method, the substrate may be fired at an elevated temperature to complete transformation of the as dipped layers into the transparent thin films prior to applying the next transparent thin film layer, or the layer of transparent electrically conductive coating.
Preferably, the angle at which the substrate is dipped in the liquid solution of precursor material is between about 5xc2x0 and 25xc2x0 to the vertical.
In other aspects, successive layers may be added to the layers on each side of the substrate by dipping the substrate in a liquid solution of a desired precursor material for those additional thin film layers while maintaining the substrate coated with the first layers at an angle to the vertical. Preferably, such additional layers are formed prior to application of the transparent electrically conductive coating on the last of the transparent thin film layers on the first or the second surface or both surfaces. Also, the angle at which the substrate is maintained while dipping to add such additional layers is preferably between about 5xc2x0 and 25xc2x0 to the vertical.
Accordingly, the present invention provides a reduced glare, conductively coated panel and a method for manufacturing same which allows preparation of each of the two sides of a substrate differently through the use of a lesser expensive, more highly efficient wet deposition process so that one side of the substrate is prepared to receive an additional electrically conductive coating layer so as to maximize light transmission through the coated substrate when such conductive coating is included.